October 07, 2011

Major population expansion in mtDNA of East Asians

Major Population Expansion of East Asians Began before Neolithic Time: Evidence of mtDNA Genomes

Hong-Xiang Zheng et al.

It is a major question in archaeology and anthropology whether human populations started to grow primarily after the advent of agriculture, i.e., the Neolithic time, especially in East Asia, which was one of the centers of ancient agricultural civilization. To answer this question requires an accurate estimation of the time of lineage expansion as well as that of population expansion in a population sample without ascertainment bias. In this study, we analyzed all available mtDNA genomes of East Asians ascertained by random sampling, a total of 367 complete mtDNA sequences generated by the 1000 Genome Project, including 249 Chinese (CHB, CHD, and CHS) and 118 Japanese (JPT). We found that major mtDNA lineages underwent expansions, all of which, except for two JPT-specific lineages, including D4, D4b2b, D4a, D4j, D5a2a, A, N9a, F1a1'4, F2, B4, B4a, G2a1 and M7b1'2'4, occurred before 10 kya, i.e., before the Neolithic time (symbolized by Dadiwan Culture at 7.9 kya) in East Asia. Consistent to this observation, the further analysis showed that the population expansion in East Asia started at 13 kya and lasted until 4 kya. The results suggest that the population growth in East Asia constituted a need for the introduction of agriculture and might be one of the driving forces that led to the further development of agriculture.

9 comments:

The end of the Younger Dryas spurned population explosion. Who would have thought?

It is very, very strange that these two signatures (the other one being the neolithic agricultural expansion) cannot be clearly delineated. You would think that in every haplogroup you study, there should be two very distinct signatures (or just one, but properly timed, depending on who participated/migrated).

There is nothing surprising in the results if they are true. Continuous population growth that may have followed the rise of the temperature with the closing of the last ice age may have triggered the birth of agriculture and Neolithic and may have also driven the further development of them. Of course, agriculture may have given opportunity for further population growth and hence expansion, but that does not explain the pre-agriculture/Neolithic population growth and the ensuing population expansion if the population growth and expansion time estimations of the paper are correct. If the results are correct, we need to re-evaluate our presumptions about the relationship between population growth/expansion and agriculture not just in East Eurasia but in West Eurasia and elsewhere in the world as well.

If the results are correct, we need to re-evaluate our presumptions about the relationship between population growth/expansion and agriculture not just in East Eurasia but in West Eurasia and elsewhere in the world as well.

Onur,

I am sure there are huge regional differences. For example in Europe, in parts of the north you went from zero population to a reasonably high density supported by hunting and extensive seafood exploitation after the Younger Dryas. That same area only supported agriculture very late, and not at huge densities, and at times failing during cold periods. At mid-latitudes, the steppe/ mixed grasslands at first allowed a sizable population due to abundant grazing animals, but later heavy forestation surely meant thinner populations, away from major rivers and lakes (fishing). But even there agriculture proceeded in steps, with ever wider expansion into less fertile soils and higher altitudes, and better practices over time. So, basically, agriculture allowed continued growth rather than just a single explosion and early saturation (which may describe LBK, though).

That's what I found strange. In a region as large as China, with all its variety of habitat, surely there would be variation in the timing of various expansions.

"Continuous population growth that may have followed the rise of the temperature with the closing of the last ice age may have triggered the birth of agriculture and Neolithic and may have also driven the further development of them".

True. But that population growth is likely to have been confined to a particular region in the beginning.

But that population growth is likely to have been confined to a particular region in the beginning.

Not necessarily. If the results of the paper are correct; all areas that became temperate enough when the last ice age was closing and after may have immediately experienced population growth, but probably only in the areas with the biggest population growth (probably because they were the most temperate then) agriculture and Neolithic spontaneously began rather than being introduced from outside. But your scenario is worth studying too.

"all areas that became temperate enough when the last ice age was closing and after may have immediately experienced population growth"

But much of China isn't exactly 'temperate'. The south is tropical or subtropical and the north is cooler than temperate.

"agriculture and Neolithic spontaneously began rather than being introduced from outside".

Quite possibly true, although some see an SE Asian source. The paper may be of some value in showing the Neolithic may have been a consequence of, rather than a prerequisite for, population expansion though. From the paper:

"further analysis showed that the population expansion in East Asia started at 13 kya and lasted until 4 kya".

That does include much of the Neolithic. Another interesting little fact is that even the most derived haplogroups are widespread. Look at F1a1'4 and M7b1'2'4 for example. And haplogroup frequencies are remarkably similar across all regions, with one or two exceptions. To me this suggests that the actual 'geographic' expansion is more recent than the 'haplogroup' expansion. If the geographic expansion was as old as 10k one would expect to see geographic differentiation within the haplogroups.

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